Illuminated instrument



F. J. METZGER aILLUMINATED INSTRUMENT Jufiy 14, 1925.

Filed may 25, 1922 IN VEN TOR b2 i I LATTORNEY;

Patented July 14, 1925.

7 UNITED STATES PATENT OFFICE.

FLOYD J. METZGER, OF NEW YORK, N. Y., ASSIGNOR TO AIR REDUCTION COMPANY, INCORPORATED, A CORPORATION OF. NEW .YORK.

ILLUMINATED INSTRUMENT.

Application filed May 23, 1922. Serial No. 562,939.

To all whom it may concern: Be it known that I, FLOYD J. Mn'rzenn,

a citizen of the. United States, residing at New York, in the county of New York, State of New York, have invented certain new and useful Improvements in Illuminated Instruments; and I do hereby declare.

the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which 'it appertains to make-and use the same.

' This invention relates to gauges or measuring instruments, and particularly to the illumination of devices of this character whereby the same may be rendered visible in the dark.

An object of the invention is to provide a simple and inexpensive illuminated temperature or pressure gauge, and particularly the provision of means whereby the illumination may be obtained with a minimum expenditure of electric current.

A special application of the invent-ion is in thermometers such as are employed to indicate temperature of the circulating liquid in cooling systems for internal combustion engines.

being. generally applicable to thermometers, barometers and other measuring instru ments.

The invention depends upon the use of a gaseous medium of high electrical conductivity which maybe caused to glow by an electrical discharge resulting from the passage of a high tension current through the gas. Any suitable gas maybe employed, although gases such as neon and'helium are preferred because of their low dielectric strength which permits of the illumination with an extremely small amount of current. It isto be understood, however, that vacuum tubes containing air, carbon dioxide, nitrogen, argon or other gases under reduced pressure may be employed, provided sufiicient current is available toensure the proper illumination.

The high tension current may be obtained from any suitable source. as, for example, an ordinar induction coil, the primary circuit of which is sup lied with current from a suitable source. he high tension current It is to be observed, however, that the invention is not limited to such use,

generated by the induction coil may be delivered directly to a glow vessel containing the gas. In the special application of my invention the high tension current is.

derived from the ignition system of the engine, and I have discovered that suflicient current for the purpose may be supplied from the ignition system. The. amount of current supplied to the glow vessel may be regulated by the interposition of a properly proportioned choke coil or condenser between a high tension conductor of the ignition system and the illuminating device, and the surplus energy usually present in ignition systems may be utilized without detrimental efiect upon the operation of the enine. In the preferred embodiment of the invention the condenser is connected to a terminal of one of the spark plugs and of course several condensers may be employed and connected to the several spark plugs so that a more or less continuous illumination is efiected. If asingle spark plug is connected to the illuminating device a flash will be observed at each instant when the par ticular plug is supplied with current.

In the accompanying drawing I have illustrated the preferred embodiments of the invention, it being understood, however, that the details may be varied'and that the drawing is illustrative merely. In the drawing,

Fig. 1 is an elevation partially in section illustrating the temperature gauge adapted for use in connection with the cooling system of an internal combustion engine;

Fig. 2 is a transverse section through the structure illustrated in Fig. 1;

Fig. 3 is a diagrammatic illustration of an electrical circuit embodying the device;

Fig. 4 is a similar illustration of another electrical circuit; and

Figs. 5and 6 are details in section of different forms of the illuminating device.

Referring to the drawing, 5 indicates a frame which may be circular in form and which is ada ted to be supported on the usual cap 6 w ich closes the radiator filling spout 7 of the cooling system. The frame 5 terminates in a housing 8 which passes through an opening in the ca 6 and is secured thereto by a nut 9, t us rigidly holding the de ice in assembled relation with the cap. A thermometer 10 is supported in the frame 5, the lower or bulb end (not shown) of the thermometer being preferably embedded in a suitable cement Within the housing 8. The thermometer is of the. usual type containing mercury or heat-sensitive liquids such as xylol or alcohol which ascend the capillary bore 11 of the thermometer. A scale 12 is supported in the frame 5 behind the thermometer 10 and may bear suitable graduated marks whereb the thermometer readings are interprete The scale 12 is preferably provided with an opening 13 near the upper end of the thermometer which indicates the danger zone. A shell 14 is supported on the frame 5 at the rear thereof and behind theopening 13 in the scale 12. Within the shell 14 provide a tube 15 of some transparent mate.- rial such as glass which contains a gaseous medium, preferably neon or helium. The neon or helium may be under reduced pressure, preferably from 10 mm. to one half atmosphere, and if a vacuum tube containing air, carbon dioxide, nitrogen, argon or other gases is used, the pressure should be considerably lower. The tube 15 is provided at one end'with an electrode or mass of metal wool 16 which is connected by an insulated provided with an electrode or mass of metal wool 18 which is connected by a. conductor 18 to the shell 14. Metal foil may be em- J ployed in place of the metal wool or a coat mg of metal may be deposited upon theend of the 'tube 15. The metal wool, foil or coating at the end opposite the electrode is referably grounded, but if a sufficient surace is provided the dispersive effect will result in the completion of the circuit even though a direct connection through the frame is not provided.

The current may be supplied, for example, from an induction coil 19, the primary of which is connected by conductors 20 and 21 to a source of current 22. The high tension current generated inthe secondary may be delivered throughv a conductor 23 to the electrode 16 in the tube 15 and is thence dispersed or conveyed to the ground through a conductor 24. The opposite high tension terminal of the coil 19 is connected to the ground by a conductor 25. A circuit closer 26 is disposed in the conductor 20 so that current may be sup lied for the purpose of i1- luminatmg the thermometer as may be desirable.

' In Fig. 4 the diagrammatic illustration shows a circuit adapted for use in connection with the high tension ignition system .of an internal combustion engine, this being the preferred embodiment of the invenground by a conductor 34. This arrangement is particularly well adapted for use in producing the desired. illumination. The

high tension current is necessarily employed in the ignition system and suflicient current can be sup lied therefrom to illuminate the tube without interfering with the operation of the engine. This avoids the necessity of providing a separate source of high tension current.

In Fig. 5 of the drawing a modification of the invention is illustrated in which a tube 35 is disposed in a suitable insulated casing 36 with its ends surrounded by conducting material having a considerable elec-'- trical capacity such as metal wool 37. Metal foil or coatings of metal upon the ends of the tube may be employed in place of the metal wool. ed to a metallic contact 38 which in turn engages the capacity medium at one end of the casing 36. The other end need not be connected directly to the ground since the dispersive effect is suflicient. to ensure opera: tion of the tube.

In Fig. 6-.of thedrawing another form of the invention is illustrated, in which: a tube 39 is provided with an electrode 40 at one The conductor 17 is connect-- end projecting through the wall of the tube into the interior thereof. The tube is sur-' rounded by an insulated casing 42 and the insulated conductor 17 is connected to an electrode 40. The. opposite end .of the tube is surrounded by'a capacity medium such as 'metal wool, metal foil or a coating ofmetal.

invention or sacrificing any of the advantages thereof.

I claim:- I In a temperature indicatorfor the cooling system of an internal combustion engine 'lll provided with sparking' terminals, the comtacle respectively to one of the sparking bination of a temperature-responsive device, terminals an t0 he ground, said means ina scale behind the device having an openeluding metal W001 t t e n of he r 10 ing therein, a casing behind the scale having ceptacle- 5 a corresponding opening, ages-containing III tlmony whereof I afiix my signa receptacle withinthe casing and means for electrically connecting the ends of the recep- METZGER. 

